The present invention relates to a device to be used after a rough sorting of household refuse. It applies to the processing of the lighter part of said household refuse.
An object of the present invention is to reduce the rate of contaminants contained in said lighter part of the household refuse so that this material may be accepted for the processing cycle of paper mills. Practically, the cleaning operation performed by the device reduces the contaminant rate from a value of the order of 35% to a value close to 12%.
A further object still of the invention is to provide a device allowing continuous discharge of the separated contaminants in order to avoid periodic stops of the device for cleansing and removal of the contaminants.
A further object of the invention is to achieve the cleansing operation in an apparatus of simple construction which is robust and reliable, and in which the shredding and lacerating operations of the product are effectively performed at room temperature without introduction of media other than the water necessary for wetting the material to be processed.
For achieving these objects, the extraction device according to the invention comprises the following means taken in combination:
A drum of general cylindrical shape, with its axis horizontal, or substantially inclined in relation to the horizontal, driven in slow rotation in a certain direction, PA1 A rotor, placed inside the drum, with its axis parallel or coinciding with the axis of the drum, driven in fast rotation in a direction which is the reverse of said certain rotation direction and provided on its peripheral surface, on at least part of its length, with shredding teeth, PA1 A feed-hopper placed at one end of the drum, PA1 And a fixed plate forming a chute for the contaminants, placed at the other end of said drum.
Preferably, the rotor is of cylindrical shape, but it can also have a generally conical shape tapering towards the feed side of device.
The shredding teeth are each made of a portion of a V-shaped bar protruding at the periphery of the rotor, the point of the profile section being oriented in the direction of rotor rotational movement.
The teeth are inclined at an angle .alpha., close to 45 degrees, relative to the rotor radius passing through the base of a tooth.
Preferably, on a first portion of its length from the feed side, the rotor is provided at its periphery only with cutting fingers. Said cutting fingers are made each of a substantially rectangular plate iron, protruding at the rotor periphery in a plane which is perpendicular to the rotor axis, the front or leading edge of the plate being a cutting edge.
According to another embodiment, there is provided on said first portion of the rotor, instead of the shredding fingers, a projection formed as a helix with one or two turns for facilitating the introduction of the material to process.
According still to said other embodiment, the last shredding teeth placed in the region of the drum outlet are inclined relative to the rotation axis so as to act as a ventilator by forcing the air towards the rear outlet.
According to a further embodiment, a hood may be provided at the drum rear outlet and an air exhaust located at the upper part of said hood through which is introduced an exhaust stream.
Under these conditions, any light plastics in sheet form which remain at the rear of the drum are sucked upwards and recovered in the exhaust stream whereas the heavy refuse falls downwards. This arrangement allows the recovery of light plastics from the total refuse, which represents an advantage since the latter have a commercial value.
Advantageously, the drum of the device is formed with two areas of perforations extending along its length. A first area is situated on the feed-hopper side, where the perforations are small in order to previously eliminate fine contaminants such as dust. A second perforation area, follows the first one, where the perforations are larger for allowing passage of the shredded cellulosic matters while retaining the other contaminants.
It is also possible to provide a brush for cleaning the drum and a water-distributor outside and on the surface of the latter for completing the cleansing operation and wetting the material to be processed.
Preferably, sections of a helicoidal ramp are provided on the inner surface of the drum, in the vicinity of the feed side, for pushing the material to be processed towards the barrier which forms the outlet chute.
Finally, and also preferaly, there is provided a recycling conveyor-belt at the outlet of the drum, oriented towards the inlet of said drum for receiving the heavy refuse, that is unwanted materials such as heavy plastics, wood refuse, light metals, etc., as well as the insufficiently reduced matters such as very resistant wetted cardboards. Said conveyor provides a sorting between both categories of heavy refuse. Those belonging to the first category and which are only lightly adhering fall at the rear of the conveyor whereas those belonging to the second category, and which are wetted, adhere to the conveyor and are re-introduced in the reducing drum for a further processing cycle.